Grape juice is composed of 70 to 80% water, 20% carbohydrates, and 1% organic acids, phenolics, vitamins, minerals, and nitrogenous compounds. Sugars, organic acids, and phenolics provide flavor while the vitamins, minerals, and nitrogenous compounds are essential participants in the successful growth of yeast and the process of fermentation.

Finished wine has a similar composition to unfermented juice, but contains much lower levels of sugar, approximately 8 to 14% alcohol, and a wider range of minor components. Sugars are a chemical subgroup of carbohydrates, are sweet tasting, water soluble, and good sources of energy. Two six-carbon sugars, glucose and fructose monosaccharides, are the most important sugars in grape juice. They provide sweetness to the juice and will be consumed by yeast during the fermentation process. Sugar content in the juice of ripe grapes varies from 150 to 200 g/L. In unripe grapes, glucose is predominant. In ripe fruit, glucose and fructose are generally present in equal amounts with a slight variation depending upon the particular varietal. In overripe grapes, the level of fructose exceeds the concentration of glucose. During fermentation, yeast converts glucose and fructose into alcohol and carbon dioxide. The amount of alcohol produced is roughly related to the sugar content present in the original juice. Refined sugar, the disaccharide sucrose, is sometimes added during fermentation or secondary fermentation to provide additional sweetness and structure.

System Reagents Solutions for Sugars

The ability to measure and manage levels of sugar in juice or wine ensures a good final product. In wine and juice production, the amount of fructose or glucose is an indicator of quality. In wine, the content of D-glucose and D-fructose (total sugar) represents the amount of sugar available for fermentation by yeast. Too little glucose and fermentation will not happen properly. In addition, the authenticity of fruit juice is often checked using the ratio of fructose/glucose as specific natural sugar ratios exist for many fruits. Measuring sucrose can also be used to indicate total glucose, because during fermentation, yeast breaks down sucrose into glucose and fructose hen consumes the glucose followed by fructose. The amount of sucrose is calculated by subtracting the amount of free glucose from total glucose. Effective quality monitoring during different production stages improves productivity and ensures consistent products. Thermo Scientific™ System Reagents for Sugars are specifically developed for cost efficient juice and wine analysis as well as quality control. Optimized for the automated Thermo Scientific™ Gallery™ and Arena™ discrete photometric analyzer series, they offer flexibility, speed, measurement accuracy, and precision for enzymatic or colorimetric testing.